An aircraft fuselage is typically constructed as a series of longitudinally spaced circumferential frame members which define the general transversal (cross-sectional) fuselage shape, and a series of spaced stringer members running longitudinally with respect to the aircraft fuselage which contribute to the stiffness of the external skin. Together, the frames and stringers constitute a robust internal structure that provides support to the external fuselage skin.
The fuselage skin covers various members of the internal support structure and is typically formed of a single piece or separate pieces of relatively thin material joined to the internal frames and stingers with skin splice straps. The frames and stringers are attached to the skin using different techniques. Usually, the stringers are installed to the skin in an earlier stage of the manufacturing cycle, using rivets and/or adhesives, to form stiffened skin panels. In a later stage, the stiffened skin panels are spliced and attached to the frames. The corresponding segments of the frames may be installed with each stiffened skin panel, forming framed stiffened skin panels. In a subsequent stage, the framed stiffened skin panels are assembled, and the skins and frames spliced to form a fuselage section. These stages are repeated until the fuselage is constructed.
For those fuselage designs which have the frame members attached directly to the skin, there is a requirement that transverse openings need to be formed at appropriate locations to allow the stringers to pass therethrough. These openings, colloquially termed “mouse holes”, impose severe penalties on the strength of the frame members. As such, it is necessary to reinforce the frame members at the stringer openings in order to restore the frame member's original design strength.
Various techniques can be found in the prior art regarding how to structurally strengthen stringer openings formed in fuselage frame members. For example, reinforcement members have been proposed to be riveted to the frame member in the vicinity of the stringer openings. However, this prior riveting technique has the disadvantage that the frame member must be drilled in order to accommodate the rivets, thereby sacrificing some of the frame member's structural integrity and strength. Alternatively, bonding a reinforcement piece has been proposed but this technique has the disadvantage that the reinforcement piece does not possess the same material strength compared to the frame member. Prior strengthening techniques are evident in U.S. Pat. Nos. 4,310,132; 6,648,273 and 7,134,629, the entire content of each being expressly incorporated hereinto by reference.
It would be desirable if stringer openings could be reinforced without the need for riveting and/or bonding of the reinforcement piece to the frame member. It is towards fulfilling such need that the present invention is directed.